JP2874523B2 - Resin sealing method for thermal recording head - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention comprises a heating board having a heating element circuit and a driving circuit board having a driving circuit, wherein a driving IC is mounted on the heating board or the driving circuit board. The present invention also relates to a method of sealing the drive IC of the thermal recording head in which the drive IC is connected to the heating element circuit and the drive circuit via wiring portions such as bonding wires, respectively, and to resin-sealing the wiring portions.

[0002]

2. Description of the Related Art A thermal recording head used in a thermal facsimile or the like generally includes a heating substrate having a heating element circuit and a driving circuit substrate having a driving circuit at their ends. A driving integrated circuit (IC) is mounted near the bonding end of the heating substrate surface or the driving circuit substrate surface, and the integrated circuit is bonded to the heating element circuit and the driving circuit with a bonding wire. Etc. are conducted through the wiring parts such as
In this case, a flip chip bonding method or a wire bonding method is generally known as an IC mounting method.

[0003] After these bondings, in order to prevent moisture and conductive foreign substances from entering the exposed portions of the wiring material of the heat-generating substrate and the driving circuit board and the bonding portion of the driving IC, protective sealing with silicone resin is performed. Stopping is being done. Further, it is common to attach a head cover to the silicone-based sealing portion for the purpose of mechanical protection of the protection sealing portion and guide of the recording paper discharged by the platen roller. In particular, in the mounting method in the wire bonding method, the mechanical strength of the bonding wire is extremely weak even after protection and sealing with a silicone resin, so that a head cover is attached to facilitate handling during the manufacturing process, Alternatively, a jig having a head cover function is required. Also, in the flip chip bonding method,
After protection and sealing with a silicone resin or the like, a head cover is also required to mechanically protect the elements of the driving IC itself.

Conventionally, as described above, a silicone resin is mainly used as a resin used for protective sealing of such a driving IC, and the silicone resin has sufficient environmental resistance and electrical insulation. However, the function of mechanical protection is not sufficient, and a head cover must be attached to the protective sealing portion. Therefore, there is a problem that the number of working steps is large and the material cost is high.

For this reason, in order to provide the function of mechanically protecting the driving IC and the bonding wire not in the head cover but in the sealing resin itself, an epoxy having a large hardness is used instead of a silicone resin which has been generally used so far. A method of sealing with a resin composition has been developed.

However, when sealing is performed with the epoxy resin composition, the epoxy resin composition is inferior in defoaming properties as compared with the silicone resin, and therefore, voids are generated on the surface of the cured sealing resin. Such surface voids have the problem of damaging the thermal recording paper.

[0007] Further, the epoxy resin composition has a problem that the thermal stress with the substrate is large, and it is conceivable to use a high content of filler for the purpose of reducing the thermal stress. Becomes larger,
The bottom of the bonding wire on the fine heating substrate and the drive I
There is a problem that an unfilled portion is easily formed in the gap of C and voids are easily generated on the surface of the cured product.

Further, the advantages of replacing the silicone resin with an epoxy resin include the cost reduction by eliminating the head cover and the downsizing of the sealant by performing the function of the paper feed guide. Is required to have shape controllability.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has a good filling property and a shape controllability without causing voids on the surface of a wiring portion such as a bonding wire of an integrated circuit mounted on a thermal recording head. An object of the present invention is to provide a method for sealing a thermal recording head with epoxy resin, which can be sealed well.

[0010]

The inventor of the present invention has made intensive studies to achieve the above object, and as a result, has provided a heating board having a heating element circuit and a driving circuit board having a driving circuit. A heat-sensitive recording head in which a driving IC is mounted on the heat-generating substrate or the driving circuit board, and the driving IC is connected to the heat-generating element circuit and the driving circuit via wiring portions such as bonding wires. When the drive IC and each wiring portion are sealed with a resin, the resin sealing is performed using an epoxy resin composition having a viscosity of 480 to 2000 poise and an aspect ratio of 0.08 to 0.25, In this case, in particular, the epoxy resin composition is applied in a form of at least two lines across the wiring portions of the driving IC, the heating element circuit, and the driving circuit. It is effective to continuously integrate the linear coating portions by the flow of the resin composition, cover the entire surface of the driving IC and each wiring portion with the epoxy resin composition, and cure the resin. In addition, there is no rise of voids and the like from the lower part of the wire, so that the surface voids can be suppressed as much as possible. They have been found to be linear and function effectively as a paper feed guide, leading to the present invention. That is, the present invention includes a heating substrate having a heating element circuit and a driving circuit board having a driving circuit, and a driving IC is mounted on the heating substrate or the driving circuit board. And the heating element circuit and the driving circuit are connected to each other via a wiring portion such as a bonding wire, respectively. When the driving IC and each wiring portion of the thermal recording head are resin-sealed, the viscosity of the resin sealing is reduced. Using an epoxy resin composition having an aspect ratio of 0.08 to 0.25 at 480 to 2000 poise, the epoxy resin composition is applied across the respective wiring portions of the driving IC, the heating element circuit and the driving circuit. At least two lines are applied, and then the driving IC and each wiring portion are coated with the epoxy resin composition by the flow of the epoxy resin composition, and the coated epoxy To provide a resin sealing method of the thermal recording head, characterized in that curing the fat composition.

Hereinafter, the present invention will be described in more detail. As shown in FIGS. 1 to 5, the resin sealing method of the present invention comprises, for example, a heating board 1 having a heating element circuit (heating element) 1a and a driving board 1a. The driving circuit board 2 having the circuit 2a is joined at one end thereof, and the driving IC 3 is joined to the terminal of the driving IC 3 near the joining end of the heating substrate 1 or the driving circuit board 2 surface. Mounted along the direction, the terminals of the IC 3 and the heating element circuit 1a and the driving circuit 2
The above-mentioned IC 3 of the thermal recording head and each of the wiring portions 4 and 5 are electrically sealed with a resin through the wiring portions 4 and 5 such as bonding wires. 2 to 5, reference numeral 6 denotes a heat dissipation substrate, and reference numeral 7 denotes a sealing resin.

In such a thermal recording head, the heat-generating substrate 1 is brought into contact with a platen roller 8 to pass a thermal recording paper 9 between the heat-generating substrate 1 and the platen roller 8.

The IC 3 includes both an IC 3 mounted on the driving circuit board 2 as shown in FIGS. 1 to 3 and a IC 3 mounted on the heat generating board 1 as shown in FIGS.

According to the present invention, in such a sealing method, the sealing resin 7 has a viscosity of 480 to 2000 poise, preferably 480 to 1000 poise, and more preferably 480 to 8 poise.
00 poise, the aspect ratio is 0.08 to 0.25, preferably 0.10 to 0.22, more preferably 0.12 to 0.22.
A fluid epoxy resin composition of 0.20 is used.

In this case, the viscosity is a value at the time of application at 20 rotations using a rotor 7 with a BH-type rotor viscometer, and the aspect ratio is 0.1 g of the epoxy resin composition.
Is dropped on a glass plate and heated for 1 hour on a hot plate at 120 ° C., and the value obtained by dividing the height of the cured product by the diameter of the bottom surface.

That is, in the thermal recording head, the bonding wires on the heat-generating substrate side have a higher density than the bonding wires on the driving circuit board side. The filled portion remains to lower the reliability, and the voids rise during curing, making it difficult to obtain a sealing surface state that can be used as a paper feed guide. On the other hand, if the viscosity is too low, unfilling can be prevented, but voids generated from gaps between substrates cannot be suppressed.

On the other hand, if the aspect ratio is lower than 0.08, a part of the bonding wire is exposed, or a portion which does not need to be sealed is sealed.
In some cases, the original operation of the thermal recording head device may be hindered. On the other hand, when the aspect ratio exceeds 0.25, the shape of the sealing portion after curing becomes unsuitable as a paper feed guide.

As such an epoxy resin composition,
Liquid at room temperature is effective. As the curable epoxy resin constituting the liquid epoxy resin composition, a resin having two or more epoxy groups in one molecule can be used, as long as it can be cured by various curing agents as described below. There are no particular restrictions on the molecular structure, molecular weight, and the like, and various conventionally known compounds can be used. Specifically, for example, epoxy resins synthesized from various novolak resins including epichlorohydrin and bisphenol, alicyclic epoxy resins or epoxy resins into which halogen atoms such as chlorine and bromine atoms have been introduced, and the like, Among them, a glycidyl ether derivative of bisphenol A or bisphenol F is preferably used in order to obtain a low-viscosity composition that is liquid at room temperature. In addition, the use of the epoxy resin is not necessarily limited to one type, and two or more types may be mixed and used.

When using the above epoxy resin, a monoepoxy compound may be appropriately used in combination.
Specific examples of the monoepoxy compound include styrene oxide, cyclohexene oxide, propylene oxide, methyl glycidyl ether, ethyl glycidyl ether, phenyl glycidyl ether, allyl glycidyl ether, octylene oxide, dodecene oxide and the like.

Examples of the curing agent include amine curing agents such as diaminodiphenylmethane, diaminophenylsulfone, and metaphenylenediamine; and acids such as phthalic anhydride, pyromellitic anhydride, and benzophenonetetracarboxylic anhydride. Examples thereof include anhydride-based curing agents and phenol novolac curing agents having two or more hydroxyl groups in one molecule, such as phenol novolak and cresol novolak. Among these, an acid anhydride-based curing agent is preferably used to obtain a low-viscosity, low-stress epoxy resin composition.

The amount of the curing agent used can be a usual amount, but is preferably in the range of 50 to 150 equivalent%, particularly preferably 80 to 110 equivalent%, based on the epoxy group equivalent of the epoxy resin.

Further, in the epoxy resin composition, for the purpose of accelerating the reaction between the curing agent and the epoxy resin,
Various curing accelerators, for example, imidazole or a derivative thereof, a tertiary amine derivative, a phosphine derivative, a cycloamidine derivative, and the like can be used in combination.
In addition, the compounding quantity of these hardening accelerators can also be made into a normal range.

Further, an inorganic filler can be blended in the epoxy resin composition. In this case, the kind of the inorganic filler to be used, a single use or a combination of a plurality of kinds is not limited, and is appropriately selected. Examples of the inorganic filler include one or two selected from natural silica such as crystalline silica and amorphous silica, synthetic high-purity silica, synthetic spherical silica, talc, mica, silicon nitride, boron nitride, and alumina. The above can be used.

The amount of the inorganic filler is determined so that the viscosity and the aspect ratio of the epoxy resin composition fall within the above ranges.

The epoxy resin composition may further contain a releasing agent such as a stress reducing agent, a carbon-functional silane for improving adhesion, waxes, fatty acids such as stearic acid and metal salts thereof, and a pigment such as carbon black, if necessary. , Dyes, antioxidants,
A surface treatment agent (such as γ-glycidoxypropyltrimethoxysilane), various conductive fillers, a thixotropic agent, and other additives can be blended. In particular, as the thixotropy-imparting agent, it is preferable to use finely divided spherical silica having an average particle size of 5 μm or less, and more preferably to use spherical silica having an average particle size of 2 μm or less.

The epoxy resin composition can be obtained by uniformly stirring and mixing predetermined amounts of the above-mentioned components (the order of blending the components is not particularly limited). In this case, if necessary, it may be diluted with an organic solvent such as acetone, toluene, xylene or the like before use.

The viscosity of the epoxy resin composition and the above-mentioned aspect ratio can be controlled by appropriately selecting the type of the epoxy resin and the curing agent, the type of the filler or the thixotropy-imparting agent, and particularly the amount of the epoxy resin and the curing agent. Further, for example, a syringe or a needle for discharging the epoxy resin may be heated to lower the viscosity to 2000 poise or less, or may be heated before or after coating the substrate to 2000 poise or less.

The cured product of the epoxy resin composition preferably has a hardness of at least Shore D60, particularly at least Shore D80.

In the present invention, when resin sealing is performed using the above-described epoxy resin composition, the epoxy resin composition is applied across the wiring portions of the driving IC, the heating element circuit, and the driving circuit. At least two lines, and then the linear application parts are continuously integrated by the flow of the epoxy resin composition, and the entire driving IC and each wiring part are coated with the epoxy resin composition and cured. Is recommended.

More specifically, in FIG. 1, at least the wiring section 4 on the heat generating board side and the wiring section on the driving circuit board 2 side along the bonding direction of the bonding portion 10 between the heat generating board 1 and the driving circuit board 2. The two linear coating portions that respectively traverse the portion 5 are applied while being separated from each other, and an application method shown in FIG. 6 is an example of the mode (in FIG. 6, 11 is a linear coating portion). The number of the linear coating portions 6 may be two or more.
In addition to the two wires that cross the wiring portions 4 and 5, a linear coating portion 6 can be formed on the IC 3 (FIGS. 6A and 6B). In this case, especially when sealing the IC 3 last,
When applying resin linearly between the linear application parts,
It is permissible to use a resin having an aspect ratio of 0.08 or less as this resin.

By the application as described above, each linear application portion flows and spreads in the width direction thereof, and is integrated with each other to cover the entire surface of the IC and each wiring portion. By using an epoxy resin composition having a specific ratio, the epoxy resin composition flows, spreads and integrates well before curing, thereby reducing voids and reducing unfilled portions, thereby ensuring shape controllability.

It should be noted that there is no limitation on the type, application method, application conditions, application sequence, and the like used for application.

In this case, since the wiring densities of the bonding wires on the heat-generating substrate side and the driving side are different, it is also effective to use an epoxy resin composition for covering them with different viscosity and the like according to the wiring density. Also, as described above, the order is not limited, and as a method of improving the filling property, after partially or several coatings, leaving at room temperature or while heating, or pre-curing, sealing, and then sealing the remaining portion. Can be also adopted.

The conditions for curing the epoxy resin composition are not particularly limited, but the composition is initially cured at a temperature of 80 to 100 ° C. for 30 minutes to 1 hour, and then cured at 120 to 1 hour.
It is preferable to perform the main curing at 75 ° C. for 2 to 5 hours.

[0035]

EXAMPLES The present invention will be specifically described below with reference to examples and comparative examples, but the present invention is not limited to the following examples. In addition, in the following examples, a part shows a weight part. <Preparation of Epoxy Resin Composition> 41.9 parts of bisphenol type epoxy resin (epoxy equivalent: 184, viscosity at 25 ° C .: 160 poise), 42.9 parts of acid anhydride (4-methylhexahydrophthalic anhydride), the following formula 11.2 parts of the silicone-modified epoxy resin represented by (1), 3 parts of an imidazole-based curing accelerator (trade name: HX3741, manufactured by Asahi Kasei Corporation),
1 part of γ-glycidoxypropyltrimethoxysilane, fused spherical silica having an average particle diameter of 1 μm or less as a thixotropy-imparting agent and fused spherical silica having an average particle diameter of 15 μm as an inorganic filler were blended in the amounts shown in Table 1, Were uniformly mixed to obtain epoxy resin compositions A to H.

[0036]

[Table 1]

[0037]

Embedded image

Next, using the epoxy resin composition shown in Table 1, the thermal recording head shown in FIG. 7 was sealed at the needle positions shown in Tables 2 and 3 among the needles 12 shown in FIG. Further, the thermal recording head shown in FIG. 8 was similarly sealed at the positions shown in Tables 4 and 5 among the needle positions shown in FIG.

The sealing conditions are as follows. Thermal recording head: long piece length 5 cm, 6 driving ICs mounted, heating substrate side wire spacing 80 μm, chip spacing 10
Model of use of 00 μm resin ejection device: Auto shooter (manufactured by Iwashita Engineering Co., Ltd.) Needle inner diameter: 1.25 mm Distance from needle tip to upper part of chip: 500 μm Coating speed: 30 mm / sec Curing condition: 2 on 150 ° C. hot plate The following evaluation was performed on the sealed thermal recording head. The results are shown in Tables 2 to 5. <Surface Void Occurrence State> The number of voids (including penetrating voids) on the surface of the sealant was observed and evaluated according to the following criteria. ：: 0 ×: 1 or more <Void lower part generation state> The sealant was cut with a slicer, and the number of unfilled parts and void generation in the lower part of the heating element side wire was observed, and evaluated according to the following criteria. ：: 0 pieces ×: 1 piece or more <Wire sealing state> The presence or absence of exposure of the bonding wire on the surface of the sealant was observed. ：: no exposure ×: there is an exposed portion <Sealant shape control> As shown in FIG. 9, the angle of the tangent at the edge of the sealing resin 7 on the side of the heat generating substrate 2 when the resin sealing length is 7 mm. is good (○), where θ is 50 to 15 ° and both ends of the sealing resin 7 are substantially parallel to the joints 10 respectively.
And the others were regarded as defective (x).

[0040]

[Table 2]

[0041]

[Table 3]

[0042]

[Table 4]

[0043]

[Table 5]

[0044]

According to the resin sealing method for a thermal recording head of the present invention, a wiring portion such as a bonding wire of an integrated circuit mounted on the thermal recording head is filled with an epoxy resin composition with good filling properties and a void is formed on the surface. , And can be sealed in a small size with good shape controllability.

[Brief description of the drawings]

FIG. 1 is a plan view showing an example of a thermal recording head to which the present invention is applied.

FIG. 2 is a cross-sectional view illustrating an example of a thermal recording head to which the method of the present invention is applied.

FIG. 3 is a cross-sectional view showing an example of a thermal recording head to which the method of the present invention is applied.

FIG. 4 is a cross-sectional view showing an example of a thermal recording head to which the method of the present invention is applied.

FIG. 5 is a sectional view showing an example of a thermal recording head to which the method of the present invention is applied.

6 (a) to 6 (e) are plan views each showing a resin application mode according to the sealing method of the present invention.

FIG. It is sectional drawing which shows the thermosensitive recording head and needle position in case of resin sealing of 1-17.

FIG. It is sectional drawing which shows the thermosensitive recording head and needle position in case of 18-34 resin sealing.

FIG. 9 is a cross-sectional view illustrating a method for evaluating the shape controllability of a sealant.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Heat generation board 1a Heating element circuit 2 Driving circuit board 2a Driving circuit 3 Driving IC 4, 5 'Wiring part 6 Heat radiation board 7 Sealing resin 8 Platen roller 9 Thermal recording paper 10 Bonding part 11 Linear coating part 12 Needle

──────────────────────────────────────────────────続 き Continuing on the front page (72) Kazuo Dobashi 1-10 Hitomi, Matsuida-machi, Usui-gun, Gunma Prefecture Inside Silicone Electronics Materials Research Laboratory Shin-Etsu Chemical Co., Ltd. (72) Takayuki Sawada Matsui, Usui-gun, Gunma Prefecture Hitomi Tamachi 1-10 Shin-Etsu Chemical Co., Ltd. Silicone Electronic Materials Research Laboratory (56) References JP-A-4-267162 (JP, A) JP-A-61-268464 (JP, A) JP-A 62 −46536 (JP, A) Hira 2-99649 (JP, U) (58) Fields investigated (Int. Cl. ⁶ , DB name) B41J 2/335 B41J 2/345

Claims (2)

(57) [Claims] 1. A heating board having a heating element circuit and a driving circuit board having a driving circuit. A driving IC is mounted on the heating board or the driving circuit board. When the drive IC and each wiring portion of the thermal recording head, in which the heating element circuit and the drive circuit are respectively connected via wiring portions such as bonding wires, are resin-sealed, the resin sealing has a viscosity of 480.
~ 2000 poise and aspect ratio 0.08 ~ 0.25
The epoxy resin composition is applied in at least two lines across the respective wiring portions of the driving IC, the heating element circuit and the driving circuit, and then the epoxy resin composition A resin sealing method for a thermal recording head, characterized in that a driving IC and each wiring portion are covered with the epoxy resin composition by the flow of an object, and the coated epoxy resin composition is cured. 2. The method according to claim 1, wherein the epoxy resin composition contains a glycidyl ether derivative of bisphenol A or bisphenol F, an acid anhydride-based curing agent, and an inorganic filler.